[82.08] Rapid Rotation Above and Below the Substellar Boundary

G. Basri (UC Berkeley)

I present the results of a multiyear survey of very low mass
stars and brown dwarfs, at high spectral resolution. The
echelle spectra were gathered with the HIRES spectrometer at
the Keck Observatory. One primary purpose was to determine
rotational velocities for many objects of the late M and L
spectral classes. Some of these objects are confirmed brown
dwarfs, others are stars near the bottom of the main
sequence, and some might be either. I show that the initial
indication provided by BRI 0021, that such objects tend to
be rapidly rotating and display little H-alpha emission,
proves to be a common characteristic. There is a general
trend to higher rotation velocities as one looks to objects
of lower luminosity; the fastest rotator found so far is the
brown dwarf Kelu-1 at 80 km/s (which implies a rotation
period of about 90 minutes!). The most active object, PC
0025 (which may well be a brown dwarf), is a relatively slow
rotator and probably very young. I discuss a possible
explanation for these results: the dynamos for these objects
are fully turbulent, driven by convection (and therefore
indirectly by the object's luminosity), and quenched when
the rotational velocities become too fast in comparison to
the convective velocities. I thank the NSF for its support
through grant AST96-18439.

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